This invention relates in general to fluorinated dimethyl ethers and specifically to methyl difluoromethyl ether as a starting material for the synthesis of fluorinated dimethyl ethers. Such fluorinated dimethyl ethers, including bis(difluoromethyl)ether (CHF.sub.2 OCHF.sub.2), have utility has CFC alternatives, particularly for use as refrigerants, blowing agents, etc.
Bis(difluoromethyl)ether has been prepared previously by chlorination of dimethyl ether followed by isolation and fluorination of bis(dichloromethyl)ether. The chlorination step resulted in a complex mixture of chlorinated dimethyl ethers, some of which were unstable, e.g. to distillation, from which bis(dichloromethyl)ether was separated. Moreover, chloromethyl methyl ether and bis(chloromethyl)ether are produced by this reaction, and are carcinogens.
Another approach to the synthesis of methyl difluoromethyl ether is disclosed by Hine and Porter in Methylene derivatives as intermediates in polar reaction VIII. Difluoromethylene in the Reaction of Chlorodifluoromethane with Sodium Methoxide, published in the Journal of the American Chemical Society 79, 5493-6 (1957). This article describes a reaction mechanism wherein the desired difluoromethyl-methyl-ether is synthesized in a batch reaction in a fixed ratio with the by-product trimethyl-orthoformate, while continuously refluxing the unreacted feed. However, not only does this reaction produce large amounts of trimethylorthoformate, but also the product itself breaks down to trirnethylorthoformate, resulting in less than advantageous yields of the desired difluoromethyl methyl ether.
U.S. Pat. No. 5,185,474, the disclosure of which is hereby incorporated by reference, discloses avoiding the production of such carcinogens and unstable compounds by using methyl difluoromethyl ether as a starting material. The methyl difluoromethyl ether is chlorinated to produce a reaction mixture including at least one compound of the formula CF.sub.2 HOCH.sub.3-z Cl.sub.z, wherein z is 1, 2, or 3. The mixture can then be fluorinated, or any one of the chlorination compounds first separated from the mixture and separately fluorinated.
However, during the chlorination of CF.sub.2 HOCH.sub.3, it is difficult to control the distribution of products. Although manipulation of the molar flow rates of Cl.sub.2 and CF.sub.2 HOCH.sub.3 can give a slight predominance of CF.sub.2 HOCH.sub.2 Cl or CF.sub.2 HOCHCl.sub.2, a significant amount of CF.sub.2 HOCCl.sub.3 is formed. If the desired product to be subsequently fluorinated is either CF.sub.2 HOCH.sub.2 Cl or CF.sub.2 HOCHCl.sub.2, the formation of CF.sub.2 HOCCl.sub.3 causes a considerable reduction in the efficiency of the process.
Accordingly, it is an object of the present invention to provide an improved process for the production of bis(difluoromethyl) ether.
It is an further object of the present invention to provide an improved process for the production of bis(difluoromethyl) ether wherein the various required separations may be effected by distillation without loss of yield and danger of explosion due to marked instability of the various intermediates.
It is a still further object of the present invention to provide a process for efficiently producing difluoromethyl methyl ether.